Locke wishes to avoid any presupposition about matter, or mind, or their relation. It is not difficult to see that the notions which he has expelled often re-enter unbidden. But the peculiar value of his psychology consists in his attempt to keep clear of them. He begins neither with mind nor with matter, but with ideas. Their existence needs no proof: “everyone is conscious of them in himself, and men’s words and actions will satisfy him that they are in others.” His first enquiry is “how they come into the mind”; his next business is to show that they constitute the whole material of our knowledge. In his answer to the former question we discover the influence of traditional philosophy, or, rather, of ordinary common-sense views of existence, upon his thought. All our ideas, he says, come from experience. The mind has no innate ideas, but it has innate faculties: it perceives, remembers, and combines the ideas that come to it from without; it also desires, wills, and deliberates; and these mental activities are themselves the source of a new class of ideas. Experience is, therefore, two-fold. Our observation may be employed either about external sensible objects, or about the internal operations of our minds. The former is the source of most of the ideas which we have, and, as it depends “wholly upon our senses,” is called “sensation.” The latter is a source of ideas which “every man has wholly in himself,” and it might be called “internal sense”; to it he gives the name “reflection.”
Hence, the peculiarity of Locke’s position. There are no innate ideas “stamped upon the mind” from birth; and yet impressions of sense are not the only source of knowledge: “the mind,” he says, “furnishes the understanding with ideas.” No distinction is implied here between “mind” and “understanding,” so that the sentence might run, “the mind furnishes itself with ideas.” As to what these ideas are, we are not left in doubt: they are “ideas of its own operations.” When the mind acts, it has an idea of its action, that is, it is self-conscious. Reflection, therefore, means self-consciousness, and, as such, is assumed to be an original source of our knowledge. Afterwards both Hume and Condillac refused to admit reflection as an original source of ideas, and both, accordingly, found that they had to face the problem of tracing the growth of self-consciousness out of a succession of sensations. According to Locke, reflection is an original, rather than an independent, source of ideas. Without sensation, mind would have nothing to operate upon, and, therefore, could have no ideas of its operations. It is “when he first has any sensation” that “a man begins to have any ideas.” [Book 2, Chapter 1, Section 23] The operations of the mind are not themselves produced by sensation, but sensation is required to give the mind material for working on.
The ideas which sensation gives “enter by the senses simple and unmixed”; [Book 2, Chapter 2, Section 1] they stand in need of the activity of mind to bind them into the complex unities required for knowledge. The complex ideas of substances, modes and relations are all the product of the combining and abstracting activity of mind operating upon simple ideas, which have been given, without any connection, by sensation or reflection. Locke’s doctrine of knowledge has thus two sides. On the one side, all the material of knowledge is traced to the simple idea. On the other side, the processes which transform this crude material into knowledge are activities of mind which themselves cannot be reduced to ideas. Locke’s metaphors of the tabula rasa, “white paper,” [The same metaphor is used by Hooker, Ecclesiastical Polity, bk. I, chap. VI: “The soul of man being therefore at the first as a book, wherein nothing is, and yet all things may be imprinted.”] and “dark room” misled his critics and suggested to some of his followers a theory very different from his own. The metaphors only illustrate what he had in hand at the moment. Without experience, no characters are written on the “tablets” of the mind; except through the “windows” of sensation and reflection, no light enters the understanding. No ideas are innate; and there is no source of new simple ideas other than those two. But knowledge involves relations, and relations are the work of the mind; it requires complex ideas, and complex ideas are mental formations. Simple ideas do not, of themselves, enter into relation and form complex ideas. Locke does not, like Hobbes before him and Hume and Condillac after him, look to some unexplained natural attraction of idea for idea as bringing about these formations. Indeed, his treatment of “the association of ideas” is an afterthought, and did not appear in the earlier editions of the Essay.
Starting from the simple ideas which we get from sensation, or from observing mental operations as they take place, Locke has two things to explain: the universal element, that is, the general conceptions with which knowledge is concerned or which it implies, and the reference to reality which it claims. With the former problem Locke deals at great length; and the general method of his exposition is clear enough. Complex ideas arise from simple ideas by the processes of combination and abstraction carried out by the mind. It would be unfair to expect completeness from his enterprise; but it cannot be denied that his intricate and subtle discussions left many problems unsolved. Indeed, this is one of his great merits. He raised questions in such a way as to provoke further enquiry. Principles such as the causal relation, apart from which knowledge would be impossible, are quietly taken for granted, often without any enquiry into the grounds for assuming them. Further, the difficulty of accounting for universals is unduly simplified by describing certain products as simple ideas, although thought has obviously been at work upon them. At the outset of his enquiry, simple ideas are exemplified by yellow, white, heat, cold, soft, hard, and so forth; but, towards the close of the second book, a very different list is given, which includes space, time, solidity, motion, power. Having arrived at this latter point, he seems to forget his view that all knowledge begins with the particular, with something “simple and unmixed.” Indeed, his whole doctrine of modes may be said to be based on oblivion of the fact that a simple idea must be really simple. Instead of showing how the idea of space is built up out of many particular sensations (or simple ideas) of particular spaces, he regards particular spaces as modes of the simple idea space; instead of showing how the idea of time is evolved from our experience of particular durations, he calls the latter modes of the simple idea time; and so on. Unwittingly, he generalises the particular. He professes to begin with the mere particulars of external or internal sense, and to show how knowledge—which is necessarily general—is evolved from them. But, instead of doing so, he assumes a general or universal element as already given in the simple idea, and then treats the particular experience as one of its modes.
Having gone so far, he might almost have been expected to take a further step and treat the perceptions of particular things as modes of the simple idea substance. But this he does not do. Substance is an idea regarding which he was in earnest with his own fundamental theory; and the difficulties in which his theory involved him on this head were both provocative of criticism and fruitful for the progress of thought. He admits that substance is a complex idea; that is to say, it is formed by the mind’s action out of simple ideas. Now, this idea of substance marks the difference between having sensations and perceiving things. Its importance, therefore, is clear; but there is no clearness in explaining it. We are told that there is a “supposed or confused idea of substance” to which are joined (say) “the simple idea of a dull whitish colour, with certain degrees of weight, hardness, ductility and fusibility,” and, as a result, “we have the idea of lead.” A difficulty might have been avoided if substance could have been interpreted as simply the combination by the understanding of white, hard, etc., or some similar cluster of ideas of sensation. But it was not Locke’s way thus to ignore facts. He sees that something more is needed than these ideas of sensation. They are only joined to “the supposed or confused idea of substance,” which is there and “always the first and chief.” He holds to it that the idea is a complex idea and so made by the mind; but he is entirely at a loss to account for the materials out of which it is made. We cannot imagine how simple ideas can subsist by themselves, and so “we accustom ourselves to suppose some substratum wherein they do subsist,” and this we call substance. In one place, he even vacillates between the assertions that we have no clear idea of substance and that we have no idea of it at all. It is “a supposition of he knows not what.” This uncertainty, as will appear presently, throws its shadow over our whole knowledge of nature.
The “new way of ideas” is thus hard put to it in accounting for the universal element in knowledge; it has even greater difficulties to face in defending the reality of knowledge. And, in the latter case, the author does not see the difficulties so clearly. His view is that the simple idea is the test and standard of reality. Whatever the mind contributes to our ideas removes them further from the reality of things; in becoming general, knowledge loses touch with things. But not all simple ideas carry with them the same significance for reality. Colours, smells, tastes, sounds, and the like are simple ideas, yet nothing resembles them in the bodies themselves; but, owing to a certain bulk, figure and motion of their insensible parts, bodies have “a power to produce those sensations in us.” These, therefore, are called “secondary qualities of bodies.” On the other hand, “solidity, extension, figure, motion or rest, and number” are also held by Locke to be simple ideas; and these are resemblances of qualities in body; “their patterns do really exist in the bodies themselves,” and, accordingly, are “primary qualities of bodies.” [A similar distinction between qualities of body was formulated by Galileo, Hobbes and Descartes; its origin may be traced to Democritus; and the words “primary” and “secondary” were occasionally used in this connection by Robert Boyle, Origine of Formes and Qualities (1666), pp. 10, 43, 100–1; cp. Tracts (1671), introduction, p. 18.]In this way, by implication if not expressly, Locke severs, instead of establishing, the connection between simple ideas and reality. The only ideas which can make good their claim to be regarded as simple ideas have nothing resembling them in things. Other ideas, no doubt, are said to resemble bodily qualities (an assertion for which no proof is given and none is possible); but these ideas have only a doubtful claim to rank as simple ideas. Locke’s prevailing tendency is to identify reality with the simple idea, but he sometimes comes within an ace of the opposite view that the reference to reality is the work of thought.